End grain direction when gluing bodyblanks

[Matt Liebenau]

Norm wasn't a luthier.
We're not making tables or houses here.

Oh I know. Just realizing where that came from. I’m pretty sure Norm was fairly responsible for propagating the “don’t squeeze all the glue out” thing that everyone loves to quote. I’ve clamped down on a lot of glue joints and never had an issue so I can get over this too.

 

[Gopherbassist]

dowel or biscuit

These words. What are these words.

 

[Lo-E]

These words. What are these words.

Using a dowel joint, one would drill holes in each half of the body that align with each other and place short pieces of dowel (round, wooden stock) in between each half to increase the gluing area and increase strength.

Using a biscuit joint applies the same principle, substituting a small, oval-shaped wafer for the dowel. The slots for these wafers are cut with a dedicated power tool called a biscuit joiner.

 

[klyph]

Standard PVA glue like Titebond can "creep" a little over time, so I've started using West epoxy for neck laminations,

Huh? West System was literally designed to “creep”- if it didn’t, most wooden boats made or repaired in the last 50 years would be in splinters. Large boat hulls have to flex, and West System, which is plastic in BOTH senses of the word, allows this.

Aliphatic resin glue also allows creep, but not NEARLY as much- it will let go, or transfer stress before allowing anywhere near the movement that epoxy does. It is also often readily reversible with modest amounts of heat, and is also water soluble in some cases.

The glues that allow the least amount of creep are derived from animal proteins.

If avoiding creep at all costs were your aim, hide glue would be your best bet. Doing a multi laminate neck that way seems like it would be a major PITA.

Have you ever had a problem with creep in necks that you have made? I would think it would take decades to manifest in an otherwise well-constructed neck, but I definitely could be wrong about that.

 

[Gilmourisgod]

I’ve never had West creep on me, definitely have with Titebond, glue lines tend to shrink over time with Titebond and telegraph a little. I’m very careful about grain orientation and good glue joints on neck, and I’m usually doing 3 or 5 piece laminates, so far so good, no creep, no telegraph.

 

[Flying B]

I also switched to west systems epoxy after I had a tightbond joint telegraph through the finish on my flying v bass. Not had that problem again since.

 

[Gary_M]

Huh? West System was literally designed to “creep”- if it didn’t, most wooden boats made or repaired in the last 50 years would be in splinters. Large boat hulls have to flex, and West System, which is plastic in BOTH senses of the word, allows this.

Aliphatic resin glue also allows creep, but not NEARLY as much- it will let go, or transfer stress before allowing anywhere near the movement that epoxy does. It is also often readily reversible with modest amounts of heat, and is also water soluble in some cases.

The glues that allow the least amount of creep are derived from animal proteins.

If avoiding creep at all costs were your aim, hide glue would be your best bet. Doing a multi laminate neck that way seems like it would be a major PITA.

Have you ever had a problem with creep in necks that you have made? I would think it would take decades to manifest in an otherwise well-constructed neck, but I definitely could be wrong about that.

I may be reading this wrong, but you may be equating creep to flexibility, and those are two different things.

When we refer to creep in adhesives, it means that some adhesives can literally migrate within the joint over time. Epoxy flexes, but to my knowledge, has no creep. PVA, on the other hand, never crystallizes the way animal protein and some other plastic resin adhesives do, but they are brittle and don’t flex like epoxy.

A multi-piece body glued with PVA could end up with either a concave or convex glue joint… and it might not..I tend to not use PVA based glues in high visibility areas for just this reason. They all have their own advantages and disadvantages and I use all of them in different scenarios.

 

[Beej]

I may be reading this wrong, but you may be equating creep to flexibility, and those are two different things.

When we refer to creep in adhesives, it means that some adhesives can literally migrate within the joint over time. Epoxy flexes, but to my knowledge, has no creep. PVA, on the other hand, never crystallizes the way animal protein and some other plastic resin adhesives do, but they are brittle and don’t flex like epoxy.

A multi-piece body glued with PVA could end up with either a concave or convex glue joint… and it might not..I tend to not use PVA based glues in high visibility areas for just this reason. They all have their own advantages and disadvantages and I use all of them in different scenarios.

Agreed - another term for this phenomenon we call creep here, is "shrinkback". The glue line shrinks below the surface exposing the line between two well-joined woods. This phenomenon basically does not happen with epoxy adhesives and it's why I use them for gluing joints I want to stay hidden.

 

[Dark Horse]

Here we are, just a bunch or creeps talking creepy talk about things that creep.

Creep.




(This is obviously a useful and important post that I’ve made. What do you expect, I’m a creep. )

 

[Bruce Johnson]

Maybe we should call it Creepback?

 

[Jazzdogg]

I may be reading this wrong, but you may be equating creep to flexibility, and those are two different things.

When we refer to creep in adhesives, it means that some adhesives can literally migrate within the joint over time. Epoxy flexes, but to my knowledge, has no creep. PVA, on the other hand, never crystallizes the way animal protein and some other plastic resin adhesives do, but they are brittle and don’t flex like epoxy.

A multi-piece body glued with PVA could end up with either a concave or convex glue joint… and it might not..I tend to not use PVA based glues in high visibility areas for just this reason. They all have their own advantages and disadvantages and I use all of them in different scenarios.

Several years ago I created a lot of bent laminations with fairly severe angles using various adhesives as a test for a chair building class. Each piece stayed in clamps for a full week after glue-up. We then created a test jig with which each glue-up could be checked over time for spring-back. A tangential light source and our fingertips were used to ascertain the extent to which laminations crept relative to one another. We commonly experienced creep and spring-back with "white" and "yellow" glues. Little to no creep or spring-back was observed with resorcinol, hide glue, or epoxy.

We were careful to use carefully selected wood which had been thoroughly dried. Unfortunately, I do not have access to the written records, which stayed with the college when I retired. But, I recall that some species, like eucalyptus, moved far more than others.

 

[Bonkersville]

To me creep is deformation under stress during a long period of time. Epoxies are viscoelastic in nature, which means they kind of behave both ways: elastic on short term, viscous on a longer time span.

To my understanding modern, good quality epoxies hide their viscous nature pretty well. To the extent they appear solid under anything larger than microscopic scale. But some of the viscosity is still there.

I remember running in this some 25 years ago when I first studied using epoxy in inlay work. People had run into issues with the epoxy filler slowly flowing over time.

But as said, that should not be a measurable problem with modern, good quality epoxies.

 

[klyph]

, it means that some adhesives can literally migrate within the joint over time

I see, you mean that the adhesive migrates even though the wood around the joint is stable. I thought that you meant the adhesive was moving with the wood, which would just be flexing. My bad. I misunderstood the term.